Short interval delay blasting device



Wfay 3,1 955 w. MANN-ETAL SHORT INTERVAL DELAY BLASTING-DEVICE Filed May 26, 1954 MIME/V7025 WILL/4M MANN e AGENT United States Patent SHORT INTERVAL DELAY BLASTING DEVICE William Mann and Gordon Towell, Brownsburg, Quebec, Canada, assignors, by mesne assignments, to Canadian Industries (1954) Limited, Montreal, Quebec, Canada, a corporation of Canada Application May 26, 1954, Serial No. 432,544

Claims. (Cl. 102-27) which consists of a high explosive core such as pentaery a thritol tetranitrate for example contained within a waterproof sheath overlaid by reinforcing coverings. This fuse has a very high velocity, detonating at approximately 21,000 feet per second. Its explosive force is such that it may be used to detonate high explosives adjacent to it in a borehole or the like.

As in other methods of detonating explosives, short interval delays are desirable with this type of fuse in order to enjoy the benefits of successive shots separated by very short periods of time. This delay has been obtained in the past by using blasting caps to initiate separate lines of detonating fuse, each line being connected to one or more charges of explosives. Delaying the detonation of the successive blasting caps by known methods resulted in the delay being transmitted to the detonating fuse and thus to the separate charges. The complexity inherent in such methods is not desirable in the field.

Devices have been proposed which are designed to be inserted in a length of detonating fuse itself to act as a delay mechanism whereby the progress of the detonation wave along a line of fuse is interrupted for a short, definite and predetermined time interval.

One proposed type employs in air gap within a metallic tube assembly as a delay device. The chance of misfire is relatively high with such a type and two or three must be connected in parallel to assure proper detonation transmission.

Other types of delay devices are uni-directional in that the detonation wave must enter the device at only one end for it to be properly delayed and re-initiated in the remaining detonating fuse. An error in directional orientation while setting up a blast in the field will result in misfire with this type.

It is an object of the present invention to provide an improved short interval delay device for use with detonatiug fuse.

It is a further object of this invention to provide a waterproof reliable short interval delay device which may be quickly and conveniently attached to two ends of detonating fuse in the field without regard to direction of propagation of the detonation wave.

According to the present invention a short interval delay blasting device adapted to be inserted between two lengths of detonating fuse may be provided which charges, each of said tubular elements having an axial core of highly exothermic fast burning gasless composition and a baffling means comprising a metallic disc provided with a hole of lesser diameter than and concentric with the core of burning composition and mounted on the inner end of saidelement and a charge of deflagrating composition located between the two metallic discs.

Preferably, the tubular casing and the impervious receptacles are made of a copper or aluminum-based alloy as are the bathing discs at the inner end of the tubular elements within the device.

The baffling discs may take the form of the bottom parts of cup-shaped receptacles which serve to hold the inner ends of the tubular elements. This modification, as well as others that suggest themselves, may be used to improve the case assembly. The important part is the disc having a small hole which is positioned between each of the tubular elements and the charge of deflagrating composition.

The explosive charges next to the inner ends of the receptacles may be drawn from any one of a number of such materials which will detonate with enough force to re-initiate the detonating fuse. Lead azide has been found to be suitable for this particular application.

The tubular elements next to the explosive charges are preferably lead tubes carrying a pressed fast burning gasless delay composition such as a /30 lead oxidesilicon mixture.

The composition which may be inserted between the two lead elements may be a deflagrating composition such as at 40/20/40 ground single-base smokeless powderpotassium chlorate-lead sulphocyanate mixture.

The invention will be more readily understood through reference to the accompanying drawing which is a representation of a cut-away sectional view lengthwise through one modification of the delay device of the invention.

In the drawing 1 is the end of a length of detonating fuse inserted in the cup-shaped receptacle 2. 3 is the tubular shell shown as being crimped to the receptacles, the crimps in turn holding the fuse in place. 4 is the explosive charge and 5 is a lead tube carrying the fast burning gasless delay composition shown at 6, while 7 is the baflle plate having a small central hole at 8. A charge of deflagrating composition is shown at 9.

In practice the detonation wave travelling along a length of detonating fuse causes the first explosive charge within a device as described to detonate. After the detonation is stopped by the bafiling means, the defiagrating composition which is ignited as a result, ignites the fast burning composition in the second element and the flame proceeds along the train until it reaches the second explosive charge causing it to detonate thereby starting another detonation wave in the remaining length of fuse.

The delay caused by the device may be conveniently controlled by the lengths of the two lead elements carrying the fast burning composition. A convenient delay interval lies between 20 and 30 milliseconds and is achieved through the use of a 0.25 inch length of element of the type described. The metal discs on the ends of these elements are used to prevent the detonation of both the end of the detonating fuse and the explosive charge to blow through instantaneously.

It is apparent that substitution may be made in the various metals and compositions used, both burning and explosive, without departing from the scope of the invention.

Having thus described our invention what we claim is:

1. A short interval delay blasting device adapted to be inserted between two lengths of detonating fuse which comprises "in combination a tubular casing, two impervious receptacles adapted to receive the ends -of said lengths of detonating fuse partially encased and supported in a symmetrical opposing relationship by the tubular casing at'the'rids the-reef, two e'ikplqs'ivechai'g es abutting the inner closed ends "of "-sa'id cepta les, two

metallic tubular elements int urmabutt'ing said explosive charges, each of said tubular 'elementsh-aving an axial core of highly exothermic fast burning g as'less composition and a baffling means comprising a metallic -disc-providedwith a hole of lesser diameter than "and concentric with the core of burning composition and mounted on the inner end of said element anda charge ofdeflagrating composition locat ed betwe'en -the two me- ='tallic'discs. v V

2. A short interval delay blasting device adapted to be inserted between two lengths'of detonat'ing-fusc which comprisesin combination -a tubular metallic cast'ing, two rntallicctips a'dapted' t'o receive the ends of said lengths of detonatingfuse partially encased and supported in 'a symmetrical' 'opposing relationship by the tubular casing at the endsthereof, two explosive charges abutting the 'inner closed ends of said cups, two tubular "lead elements abutting said explosive charges, each of said tubular lead elements having an axial core of highly of charges 1 of "lead azide.

4. A short interval delay blasting device 'as'c'laimed in claim 1 wherein'thesaid highly fezg'otheir'nicjfasf'hurning gasless composition is comprised 'of a mature of 70% lead oxidehnd 30% silicon 'metal'by weight.

5. A short interval delay blastingdevice as claimed in claim 1 wher'e'inthe said"defla"g'rating composition is comprised of a mixture of 40% ground single-base smokeless powder, 20% potassium chlorate and 40% lead sulphocyana'te by weight.

References Cited in the file of this patent FOREIGN PATENTS Great Britain vJune 21111950 Great Britain May 5, 1954 

